Styrene-butadiene rubber obtained by emulsion polymerization is synthetic rubber most widely used in the production of tires and has properties such as flat vulcanizability, stable scorch, high processability, etc.
Recently, in relation to energy efficiency, automobile fuel regulations such as the EU labeling system have been tightened, and thus research on styrene-butadiene rubber materials that can exhibit environmental friendliness, abrasion resistance and the like as a material of a tire is getting more attention.
As techniques for emulsion copolymers, various patents regarding methods of preparing styrene-butadiene copolymers or styrene-butadiene-polar monomer copolymers have been published.
For example, U.S. Pat. Nos. 3,575,913 and 3,563,946 disclose that styrene-butadiene or styrene-butadiene-acrylate copolymers are prepared with potassium persulfate or azobisisobutyronitrile in an emulsion state. Also, Patent Publication No. 1999-0077755 discloses an emulsion styrene-butadiene rubber which may be used in the production of tire treads having rolling resistance with improved traction characteristics and treadwear characteristics, and a production method thereof.
In such related art polymerization of styrene-butadiene rubber, t-dodecylmercaptan (t-DDM) is used as a molecular weight modifier, which is composed of a mixture of 35 isomers due to characteristics of the production mechanism thereof, and thus when polymerization of styrene-butadiene rubber is performed with t-dodecylmercaptan, the related art polymerization has a drawback in that it has a bad influence on the final physical properties of prepared styrene-butadiene rubber.
Accordingly, there are needs for a novel method for preparing styrene-butadiene rubber that may address the drawback of t-dodecylmercaptan, and for development of styrene-butadiene rubber with physical properties improved therethrough.